The present invention relates to catalyst compositions and processes of preparing the same and a method of using the same in olefinic polymerization and copolymerization processes.
Great efforts have been made in increasing the activity of olefinic polymerization catalysts and improving the property of the product polymer. In recent years, tetravalent titanium compounds supported by magnesium compounds have been used as a catalyst in olefinic polymerization. These catalysts have relatively high activity. The use of a supporter apparently increases the efficiency of the active centers (titanium atoms) of the catalyst. For the polymerization of .alpha.-olefins having 3 or more carbon atoms, an electron donor must be added to the solid catalyst to ensure stereospecificity of the polymers.
One method of preparing an olefinic polymerization catalyst is by grinding or pulverization. Catalysts prepared by these methods have many disadvantages, such as poor granular appearance, wide particle size distribution and low activity. Another method of preparation has been proposed to overcome these disadvantages, i.e. by first dissolving a magnesium compound in solvents and then precipitating and separating the catalyst as a solid.
Japanese Laid-Open Patent 58-183708 describes the use of a mixture of organic epoxy compounds and organic phosphorus compounds to dissolve a magnesium compound, then adding a monocarboxylic acid ester and titanium tetrahalide to form a precipitate which is then used as a catalyst in an olefinic polymerization process.
The use of these catalysts overcome some of the disadvantages of catalysts prepared by grinding or pulverization. However, the activity of the catalysts is relatively low, and during extended periods of polymerization time, the activity of the catalyst decreases significantly. Moreover, both apparent density and stereospecificity of the resultant polymers are not sufficiently high; the polymer has an unpleasant odor and the quality of polymers is affected because of the presence of a large amount of residual Cl.sup.- ions. All the above-mentioned problems remain to be solved.
Japanese Laid-Open Patent 58-83006 describes using alcohols, aldehydes, amides and carboxylic acids to dissolve a magnesium compound, then adding benzoic anhydride and a dicarboxylic acid ester to prepare a solid catalyst. Although the catalyst thus prepared has improved activity and the product polymer has better granular appearance, the process of preparing the catalyst requires severe operating conditions. The temperature for dissolving the magnesium compound is high, the rate of dissolution is slow, and the viscosity of the resultant magnesium compound solution is so high that operation is difficult. Further, the efficiency of the autoclave used for polymerization is low, and environmental pollution results from the use of large amounts of titanium tetrachloride as the starting material.